The quantitative and objective assessment of a person's mental state has broad applicability in several disciplines. For example, the measurement of intensity of pain in a person, their level of depression, their level of anxiety, or their level of happiness is of substantial use in a variety of contexts, including the monitoring of patients over time, measurement of symptom severity for medical treatment, the selection of treatment modalities or treatment dosages, and treatment development (e.g. pharmaceutical development).
Existing approaches for quantifying the intensity, severity or characteristics of mental states and symptoms have thus far relied principally on self-report using questionnaires. Examples include:
The Visual Analog Scale (VAS), in which a patient draws a mark on a line, the position of the mark indicating the level of their pain or other symptom severity, with one end indicating ‘no pain’ and the other end indicating ‘worst imaginable pain’;
The Numerical Rating Scale (NRS), in which a patient indicates their level of pain or other symptoms from 0 (no pain) to 10 (worst imaginable pain). The NRS and VAS can also be combined;
The McGill Pain Questionnaire (MPQ) a questionnaire that asks a patient to select words describing their pain from a number of groups (e.g. none/mild/moderate/severe, blinding, dull, burning, throbbing, etc.); and
The Beck Depression Inventory (BDI), a questionnaire that asks patients to rate their sadness or level of depression on a variety of questions.
Another type of approach that has been used in the past has been to use quantified stimuli, and have subjects self-report their ratings of the intensity of an applied stimulus, for example using a visual analog scale or a numerical rating scale. In these cases, subjects are not rating the intensity of their symptom (e.g. intensity of their chronic pain), they are rating the intensity of the applied stimulus. In other words, entirely cognitive or mental states or characteristics, such as pain, depression, anxiety, motivation, happiness, positive affect, desire, and the like, are not adequately addressed by existing approaches.